The present invention relates to a sealed thrust ball bearing which is useful, for example, as the strut bearing of motor vehicles.
FIG. 2 shows a known bearing of this type (see Unexamined Japanese Patent Publication SHO No. 58-124825). The illustrated bearing comprises a first race 1, a second race 2, a plurality of balls 3 rollable therebetween and an elastic seal member 4 sealing a clearance between the inner peripheral portions of the first and second races 1, 2 and a clearance between the outer peripheral portions thereof. The sealing member 4 is directly bonded by heating to the surface of the first race 1 other than the raceway 1a thereof and is integrally formed with lips 4a, 4b at its inner and outer peripheral portions for closing the inner and outer clearances between the first and second races 1, 2. The inner peripheral portion of the second race 2 is formed with a hollow cylindrical portion 2b having an annular groove 5 formed in its radially outer surface. The inner lip 4a of the seal member 4 is fitted in the groove 5, whereby the first and second races 1, 2 are fixed to each other as an assembly.
When such a sealed thrust ball bearing is to be used as a strut bearing, the races 1 and 2 are plated with a corrosion inhibitive layer, so that the seal member 4 is bonded to the surface of the plating layer with reduced bond strength. Further the races 1, 2 are hardened after press forming and therefore become distorted. The distortion creates a clearance between the race 1 and the mold during the bonding of the seal member 4, with the result that the rubber for forming the seal member 4 is likely to flow onto the raceway 1a. Further since the press-formed race 2 is machined to form the groove 5, there arises the problem that the grooved portion 5 becomes rough-surfaced to cause marked wear to the inner lip 4a of the seal member 4 by sliding contact therewith.